Disengagement and elutriation of pneumatically elevated solids



Dec. 24, 1963 w. J. CROSS, JR 3,115,370

DISENGAGEMENT AND ELUTRIATION OF PNEUMATICALLY ELEVATED souns FiledApril 18, 1961 Z/Fr ans s a f F a L/FT P/PES & 0 P. z m 0 MW r B A DUnited States Patent 3,115,370 DISENGAGEMENT AND ELUTRTATIGN 0FPNEUMATICALLY ELEVATED SGLTDS Willis J. Cross, .l'r., Media, Pa,assignor to Air Products and Chemicals, Inc, a corporation of DelawareFiled Apr. 18, 1%1, Ser. No. 103,828 8 Claims. (Cl. 3e2 5a Thisinvention relates to processing systems for effecting hydrocarbon orother chemical conversions, and particularly those systems wherein abody of frangible, granular solid contact material, such as catalyst inthe form of pellets, beads, etc, is circulated within a closed pathincluding a plurality of treating zones wherein the reactants in gaseousstate are contacted with granular material or solids gravitating in theform of a compact moving mass to effect the desired reactions. Morespecifically, the invention is directed to those processing systemswherein a continuous circulation of the granular material is maintainedby gravitational free fall and/or compact flow thereof through aconfined downflow path and subsequent pneumatic elevation of thegranular material through an upright confined lift path. Suchcirculation causes a gradual attrition of the solids, producing fineswhose removal continuously or periodically, is necessary for efficientoperation. The invention is concerned particularly with the problems ofdisengaging the granular contact material from the lift gas at the topof the lift path and of removing the small attrited particles ofgranular material, or fines, from the circulating body of solids.

A typical processing system to which the method and apparatus of theinvention may be applied is disclosed in an article entitled Houdrifiow:New Design in Catalytic Cracking, appearing in the Oil and Gas Journal,page 78, January 13, 1949.

The invention may be applied to a disengager servicing either a singlelift pipe or a plurality of lift pipes. In any case, the trajectory ofthe discharging stream or streams of solids should be such as to causethe disengaged solids to fall freely as a relatively dense mass orcurtain of solids in a low region of the disengaging zone which islaterally removed from any rapidly rising solids discharging from one ormore lift pipes. In a multiple lift disengager the discharge ends of thelift pipes may be closely grouped in one small horizontal area of thetotal disengager cross section or they may be distributed uniformlyabout the peripheral region of the disengager, for example, in a circleconcentric to its vertical axis.

Typical of the last-mentioned type are those disclosed in U.S. Patents2,813,757 to R. M. Shirk, and 2,887,341 to W. 1. Cross, In, each ofwhich discloses a multiple litt disengager comprising an elongatedcylindrical vessel, the upper portion of which contains a disengagingzone. A plurality of lift pipes discharge streams of lift gas and solidsupwardly into the lower peripheral region of the disengaging zone. Thedecrease in gas velocity resulting from the sudden expansion of flowarea upon discharge from the lift pipes into the disengager vesselcauses the substantial major portion of the solids to completelydecelerate before reaching the top region of the disengaging zone and tosettle or fall freely to the bottom of the vessel.

Because of the high lift gas velocities employed, such as a velocity of50100 ft./sec., the disengager vessel is necessarily of considerableelongation in order to provide sufficient disengaging height, that is,vertical distance in which to effect the complete gravitationdeceleration of the granular material and reversal of its direction oftravel.

Lift disengagers of the type referred to herein are generally providedwith lift gas outlet means at their 3,l 15,379 Patented Dec. 24, 1863upper end to continuously discharge lift gas relatively free of solids,especially solids of a size suitable for continued use by recirculation.It is also a common practice to install one or more battles in the topregion of the disengager vessel just below the lift gas outlet in orderto deflect random particles of solids which may have sufiicient momentumto carry them above the main stream of solids undergoing decelerationand direction reversal and which may be carried out of the system withthe discharging lift gas it they approach too closely to the lift gasoutlet through which the lift gas moves at high velocity.

One of the major problems encountered in systems which maintaincontinuous circulation of a body of granular solids is that ofattrition, resulting in the production of fines. Efficient operationrequires the discharge from the circulating body of solids ofsubstantially all or at least a major portion of those attritedparticles which are of a size smaller than the minimum acceptable size.To this end a side stream of the circulating solids is generallywithdrawn at some suitable location in the circulatory system, and thewithdrawn stream of solids is subjected to known elutriation treatmentto eliminate the fines while retaining the larger particles for returnto the circulaing body of granular material. A location which has beenfound particularly suitable for withdrawal of solids to supply theelutriator is in the disengager vessel itself, and various methods foreffecting such withdrawal and elutriation treatment are well known inthe art.

In accordance with the invention the total lift gas discharging into thedisengaging zone from the plurality of lift paths is withdrawn from thedisengaging zone at a plurality of locations. The main stream ofwithdrawn lift gas, constituting a substantial major portion of thetotal lift gas, is withdrawn at a low level within the disengaging zoneand from a location wholly within a region laterally removed from therapidly rising streams of solids discharging from the confined liftpaths. This main portion of lift gas is conveyed upwardly as a confinedstream to and through the upper end of the disengaging zone.

The inlet end of the confined path for withdrawing the major portion oflift gas from the disengaging zone is so sized as to provide a gasvelocity sufiicient to entrain the unwanted fines. Since the inlet issituated to one side of the upwardly moving, high velocity stream ofsolids the region immediately adjacent to or surrounding the inlet willcontain a concentration of free-falling solids. The confined lift pathsare arranged to discharge into the disengaging zone at a slight angle,such as up to about 15, to the vertical so that each stream of solidsemerging from a lift path will have not only the normal conical patternof discharge but also a slight trajectory toward the location of themain gas withdrawal path. Thus, a group of lift paths may be arranged todischarge so that all have a slight trajectory in the same generaldirection, as from one side of the disengager vessel to the other orfrom a central location to a side of the vessel, or a group of liftpaths may be arranged to discharge at spaced points along a peripheralcircle concentric to the vertical axis of the vessel, with a slighttrajectory toward the axis.

As the disengaged solids descend through the region immediately adjacentto or surrounding the inlet of the main gas Withdrawal path the gasmoving laterally under the perimeter of the inlet and into theWithdrawal path entrains the smaller solids and carries them upwardlyout of the vessel. Solids elu-tn'ation thus takes place in the regionsurrounding and immediately below the inlet.

The other stream or streams of lift gas, constituting, in all, a minorportion of the total lift gas, are withdrawn from the upper end of thedisengaging zone. These secondary streams are provided with suitableflow conts trol means whereby the portion of the total lift gas sowithdrawn may be regulated at will, thereby enabling a predetermined gasvelocity to be maintained within the elutriatiug zone at the bottom ofthe main gas withdrawal ath.

p For a further understanding of the invention reference may be had tothe following description and claims taken in connection with theaccompanying drawing showing a sectional elevation of a combination liftdisengager and elutriator representing one arrangement of apparatus forcarrying out the method of the invention, particularly as applied to thetype of disengager referred to in the aforementioned patents.

Referring to the single FIGURE of the drawing, rising streams of liftgas and granular material are discharged from the upper ends of aplurality of lift pipes into the lower region of an elongatedcylindrical disengager vessel 6 having a dished head 7 at its upper endand a dished tray or partition 8 at an intermediate level defining theupper and lower boundaries of a disengaging zone 9. The upper ends oflift pipes 5 converge slightly toward the axis of the vessel 6 so as todirect the streams of solids discharging from the confined lift pathstoward the central or axial region of the disengaging zone in order thatthe substantial major portion of the descending sol-ids will fall in theaxial region andhave minimum interference with the rapidly risingparticles of solids in the peripheral region of the disengaging zone 9.

A vertical pipe 16 extends downwardly into disengaging Zone 9 through acentral opening in dished head 7 and terminates at a low level therein,slightly above and concentrically within the circle of lift pipes 5. Thelower end of pipe 10 is provided with an outwardly flared or taperedsection 11 which is located well within the envelope formed by themerging streams of solids rising from the lift pipes 5. The flaredsection, however, is not essential to the successful carrying out of theinvention, and a slightly larger straight pipe providing the desiredinlet velocity may be employed. A pair of addi tional lift gas outletpipes 12 and 13 are provided at the top of the disengaging zone 9 toeither side of the central discharge pipe 10. Pipes 12 and 13 havecontrol valves 14 and 15, respectively, by which the proportion, andhence velocity, of the lift gas Withdrawn through pipe 10 may beregulated.

An inverted curved or dished bathe plate 16 is concentrically supportedby struts 17 from the underside of dished head 7 and is spaced from thetop and sides of the vessel 6. Baffle 16 is provided with a centralopening to accommodate the pipe 10 in a close fit. Thus, the total liftgas rising from the lift pipes 5 into the disengaging zone 9 iswithdrawn from the disengaging zone as three separate streams. The majorportion of the lift gas passes through the tapered section 11 and pipe10, while the remaining pontion of the lift gas passes upwardly aroundand over the sides of baflie 16 and is withdrawn in two separate streamsthrough valve-controlled discharge pipes 12 and 13. Although two outlets12 and 13 for secondary lifit gas withdrawal are disclosed, more or evena single outlet may be employed.

For any given total flow of lift gas through the disengager vessel thegas velocity in the elutriating zone 11 may be controlled by adjustingthe discharge rate of the lift gas passing through pipes 12 and 13.Since the particle-size range of the fines removed from the solidsstream descending through the region immediately about the lowerperimeter of section 11 is a function of the gas velocity in thatregion, it is possible to determine the maximum size particles to beremoved from the system by such control of the gas velocity in theelutriating region.

In a typical installation embodying the method and apparatus of theinvention, the disengager vessel 6 may be about l525 feet in diameterand the lift pipes 5 may 4 be 8-12 inches in diameter. Main draw-offpipe 10 may be 34 feet in diameter with a 6-10 foot diameter at themouth of the elutriator sectioh 11. Secondary gas outlet conduits l2 and13 may be 12. inches in diameter.

Typical gas velocities at the top of the lift pipes 5 are in the orderof about 55 ft./sec., the top of the lift being considered as the bottomof any decelerato-r section that may be provided to reduce the gasvelocity before discharge into the disengaging zone 9.

At the base or inlet end of the elutriator section 11 the gas velocitymay be in the range of about 9-15 ft./sec., increasing the velocities inthe range of about 28-47 ft./sec. at the top of pipe 10.

It is contemplated that proper elutriation may be effected bycontrolling valves 14 and 15 so that they with draw up to about 40% ofthe total lift gas from the zone 9.

Gbviously many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

What is claimed is:

l. A combination disengager-elutriator for a multiple pneumatic solidslift system comprising an upright elongated cylindrical vessel adaptedat its lower end to receive the upper ends of a plurality of lift pipes;an elongated main outlet conduit extending along the axis of said vesselfrom a level above the discharge ends of said lift pipes through theupper end of said vessel; secondary as outlet means at the top of saidvessel provided with control means for regulating the flow of gastherethrough; and an inverted dished bafile extending across the upperregion of said vessel with its perimeter just short of the walls of saidvessel to provide an annular peripheral passageway for flow of lift gasfrom the main disengaging region of said vessel to said secondary gasoutlet means, said baffle having a central opening to receive said mainoutlet conduit.

2. Apparatus as in claim 1 in which said main conduit is outwardlyflared at its lower end.

3. A combination disengager-elutriator for a pneumatic solids liftsystem comprising an upright elongated vessel; lift path means fordischarging pneumatically elevated solids and the accompanying lift gasupwardly within the lower region of said vessel; said vessel being ofsuch increased horizontal flow area with respect to said lift path meansas to cause complete gravitational deceleration of the solids and freefall thereof through a low region within said vessel laterally removedfrom the widening cone of rapidly moving solids discharging from saidlift path means; a pipe providing a main path for lift gas withdrawaldirectly upward from a location within said laterally-removed region tothe exterior of said vessel; means at the top of said vessel forwithdrawing a secondary portion of said lift gas; a baffle in the upperregion of said vessel to deflect rising solids away from the means forwithdrawing said secondary portion of lift gas; and means forcontrolling the flow of gas through the secondary lift gas withdrawalmeans to thereby control the proportion of the total lift gas flowing insaid main lift gas withdrawal path and consequently its inlet velocity,whereby the particle size range of solids withdrawn from said. vessel bysaid main gas stream is determined.

4. A combination solids disengager and elutriator for a pneumatic solidslift system adapted to circulate granular solids comprising: an uprightelongated vessel arranged to receive upwardly discharging and laterallyexpanding streams of lift gas and solids within the lower peripheralregion thereof, said vessel being of such horizontal dimensions as toreduce the lift gas velocity to below the solids supporting velocity andof such height as to effect substantially total disengagement of saidsolids from said lift gas through gravitational deceleration, and saiddischarging strcams of lift gas and solids being so directed as to causethe substantial major portion of said disengaged solids to fall freelyto the bottom of said vessel through a region of high solidsconcentration laterally remote from the expanding cones of dischargedsolids; a main conduit extending upwardly through said vessel from a lowlevel within said region of high solids concentration but above thedischarge level of said streams, said main conduit being adapted towithdraw upwardly from said vessel the major portion of said lift gaswhile providing a gas velocity in the zone surrounding and immediatelybelow the main conduit inlet suflicient to entrain and remove from saidvessel the unwanted solids fines; controllable secondary gas withdrawalmeans at the upper end of said vessel adapted to withdraw from saidvessel such portion of the total lift gas as will maintain the desiredgas velocity in the elutriation zone at the inlet end of said mainconduit; means directly below said secondary gas withdrawal means forshielding the inlet thereto against the admission of the highest risingsolids; and means for draining the disengaged solids from the bottom ofsaid vessel.

5. Apparatus as in claim 4 in which the vertical distance 6 between thesurface upon which the free-falling disengaged solids are deposited andthe inlet end of said main conduit is such as to preclude the rebound ofthe larger-size solids from said surface into the high velocity streamof gas entering said main conduit.

6. Apparatus as in claim 4 in which said secondary gas withdrawal meanscomprises a plurality of controllable flow conduits having their inletends communicating with said vessel through its upper end at locationsuniformly distributed around said main conduit.

7. Apparatus as in claim 4 in which the maximum total flow area of saidcontrollable secondary gas withdrawal means is such as to permitwithdrawal therethrough of up to about 40% of the total lift gas.

8. Apparatus as in claim 4 in which said main gas withdrawal conduit issharply divergent over a relatively short portion of its lower end.

Elkin Dec. 31, 1957 Claunch 'Oct. 31, 1961

4. A COMBINATION SOLIDS DISENGAGER AND ELUTRIATOR FOR A PNEUMATIC SOLIDSLIFT SYSTEM ADAPTED TO CIRCULATE GRANULAR SOLIDS COMPRISING: AN UPRIGHTELONGATED VESSEL ARRANGED TO RECEIVE UPWARDLY DISCHARGING AND LATERALLYEXPANDING STREAMS OF LIFT GAS AND SOLIDS WITHIN THE LOWER PERIPHERALREGION THEREOF, SAID VESSEL BEING OF SUCH HORIZONTAL DIMENSIONS AS TOREDUCE THE LIFT GAS VELOCITY TO BELOW THE SOLIDS SUPPORTING VELOCITY ANDOF SUCH HEIGHT AS TO EFFECT SUBSTANTIALLY TOTAL DISENGAGEMENT OF SAIDSOLIDS FROM SAID LIFT GAS THROUGH GRAVITATIONAL DECELERATION, AND SAIDDISCHARGING STREAMS OF LIFT GAS AND SOLIDS BEING SO DIRECTED AS TO CAUSETHE SUBSTANTIAL MAJOR PORTION OF SAID DISENGAGED SOLIDS TO FALL FREELYTO THE BOTTOM OF SAID VESSEL THROUGH A REGION OF HIGH SOLIDSCONCENTRATION LATERALLY REMOTE FROM THE EXPANDING CONES OF DISCHARGEDSOLIDS; A MAIN CONDUIT EXTENDING UPWARDLY THROUGH SAID VESSEL FROM A LOWLEVEL WITHIN SAID REGION OF HIGH SOLIDS CONCENTRATION BUT ABOVE THEDISCHARGE LEVEL OF SAID STREAMS, SAID MAIN CONDUIT BEING ADAPTED TOWITHDRAW UPWARDLY FROM SAID VESSEL THE MAJOR PORTION OF SAID LIFT GASWHILE PROVIDING A GAS VELOCITY IN THE ZONE SURROUNDING AND IMMEDIATELYBELOW THE MAIN CONDUIT INLET SUFFICIENT TO ENTRAIN AND REMOVE FROM SAIDVESSEL THE UNWANTED SOLIDS FINES; CONTROLLABLE SECONDARY GAS WITHDRAWALMEANS AT THE UPPER END OF SAID VESSEL ADAPTED TO WITHDRAW FROM SAIDVESSEL SUCH PORTION OF THE TOTAL LIFT GAS AS WILL MAINTAIN THE DESIREDGAS VELOCITY IN THE ELUTRIATION ZONE AT THE INLET END OF SAID MAINCONDUIT; MEANS DIRECTLY BELOW SAID SECONDARY GAS WITHDRAWAL MEANS FORSHIELDING THE INLET THERETO AGAINST THE ADMISSION OF THE HIGHEST RISINGSOLIDS; AND MEANS FOR DRAINING THE DISENGAGED SOLIDS FROM THE BOTTOM OFSAID VESSEL.